I'm hoping somebody will come along and explain more eloquently - and scientifically - than I can....but the vibe I get is that the "forces" are weight, thrust and RESULTANT.
The resultant can be broken down into two REACTIONS...lift and drag.
If this three force ideal is the correct one - I don't see why NASA (and many text books) call lift a "force"...which, by the way, I always have done.